The present invention relates to a position drive for a wafer carrying integrated circuit components to be tested in a testing equipment. More particularly, the invention relates to a position drive provided with means for compensation for wafer-thickness allowances.
The devices for positioning a wafer with integrated circuit components in systems for grading the wafer by testing the same are known in the art.
In the art of electronic circuits the individual integrated circuits formed on the semiconductor wafer are tested by a probe which should be accurately located on each preselected point corresponding to the circuit to be tested. It is to be understood that the positioning of the probes must be very accurate and adjustable so that different integrated circuit units can be tested. When the probes are properly oriented the wafer may be stepped from position to position so that each micro-circuit is properly located to the assigned probe for testing.
The orientation in a predetermined position may be defined as a location in accordance with XY coordinates and a vertical position defined by Z coordinate. It is to be noted that the proper vertical position of the wafers relative to the probes must be controlled in order to obtain uniform contact pressure between each probe and each circuit.
In operation of the known devices of the type under consideration, the operator examines the wafer by an optical means and rotates the support carrying the wafer to bring the integrated circuits into proper X-Y orientation. The positioning relative to Z-coordinate is made thereafter.
In the East German Pat. No. 137037 a lifting device for lifting the integrated circuit wafer is described in which uniformly distributed pressurized-air nozzles are provided arranged in the support surfaces of the lifting rods whereby the vertical movement from lower to the upper position of the support is damped.
The guides for axial movement are equipped with air bearings so that wear compensation may be obtained in the device. The disadvantage of this lifting device is that the wafer supporting plates do not turn in the operation, and the device is not able to compensate for thickness allowances of the wafers to be tested.
U.S. Pat. Nos. 4,066,943 and 3,936,743 suggest a wafer-positioning drive provided with a lifting high-speed precision chuck for quick displacement of the wafers relative to the probes+ tips. The lifting chuck is equipped with a step motor for vertical displacement, which motor is coupled with an eccentric. Upon rotation of the eccentric the chuck is moved by a suitable means between two end positions. The movement resulted from the operation of the position drive is syncronous in character. The chuck is rotated about its central axis by manually operated means.
The disadvantage of this otherwise satisfactory device is that manually operated rotation of the chuck renders it difficult to make the device automatic. Furthermore, no thickness-allowances -compensation means are suggested in the known device and it is impossible to provide for such means without extensive changing the chuck for quick lifting movement.